Muscat handed eight-match ban
"The Disciplinary Committee has determined that the player will serve an eight-match suspension," Football Federation Australia said in a statement.
Playing what is widely believed to be his last A-League season, the 37-year-old Melbourne Victory captain rugby tackled Zahra who suffered a serious ligament injury.
Muscat said he regretted the "mistimed tackle", insisting he did not intend to injure Zahra but his career has been littered with similar incidents.
Playing for Wolverhampton Wanderers in 1998, a tackle on Charlton Athletic's Matty Holmes left his opponent needing four operations on his ankle and in the same year Muscat broke Norwich City striker Craig Bellamy's leg.
Muscat's sliding challenge on Christophe Dugarry in 2001 put the French forward out of action for two months.
Three matches are left of the regular season and even if Melbourne Victory, who have seven days to appeal, reach the A-League final, Muscat will miss out.